Field of the Invention
The present invention relates to mobile communication, and more particularly, to a technique for identifying whether an adjacent base station is an isolated base station (isolated E-UTRAN).
Related Art
An isolated base station (isolated E-UTRAN) refers to an E-UTRAN that is not normally connected to an evolved packet core (EPC) or to a mobile base station (nomadic eNB (NeNB)) with an E-UTRAN function.
An isolated base station (isolated E-UTRAN) operation is used when a normal backhaul connection is restricted. The isolated E-UTRAN operation allows a base station to operate in an isolated manner without a backhaul connection in order to provide a communication function between those in charge of public safety even when a user moves out of the coverage of the E-UTRAN or a backhaul communication path is damaged. The isolated E-UTRAN operation is intended to adapt to failure and for a network to maintain a service acceptable level in an isolated base station. The isolated E-UTRAN operation is ultimately aimed at a service recovery.
An EPC refers to a core network structure in a 3GPP long term evolution (LTE) network. The EPC is an evolution of a GPRS core network and includes a mobility management entity (MME), a serving gateway (S-GW), a PDN gateway (P-GW), a home subscriber server (HSS), and the like.
In an X2 handover, a direct tunnel is created between a base station serving a user equipment (UE) and a target base station that the UE is newly to access during the handover and downlink traffic is transmitted to the UE through the tunnel. In an S1 handover, an indirect tunnel is created between a base station serving a UE and a target base station that the UE is newly to access via an S-GW during the handover and downlink traffic is transmitted to the UE through the tunnel.